Sensor circuit for controlling, detecting, and measuring a molecular complex

ABSTRACT

A device for controlling, detecting, and measuring a molecular complex is disclosed. The device comprises a common electrode. The device further comprises a plurality of measurement cells. Each measurement cell includes a cell electrode and an integrator electronically coupled to the cell electrode. The integrator measures the current flowing between the common electrode and the cell electrode. The device further comprises a plurality of analog-to-digital converters, wherein an integrator from the plurality of measurement cells is electrically coupled to one analog-to-digital converter of the plurality of analog-to-digital converters.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/603,782 entitled SENSOR CIRCUIT FOR CONTROLLING, DETECTING, ANDMEASURING A MOLECULAR COMPLEX filed Feb. 27, 2012 which is incorporatedherein by reference for all purposes.

BACKGROUND OF THE INVENTION

Advances in micro-miniaturization within the semiconductor industry inrecent years have enabled biotechnologists to begin packingtraditionally bulky sensing tools into smaller and smaller form factors,onto so-called biochips. It would be desirable to develop techniques forbiochips that make them more robust, efficient, and cost-effective.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 illustrates a single stranded DNA (ssDNA) molecule constrained ina nanopore in a cell 100.

FIG. 2 illustrates an embodiment of a cell 200 performing nucleotidesequencing with the nanopore-based sequencing by synthesis (Nano-SBS)technique.

FIG. 3 illustrates four physical states of a sensor cell.

FIG. 4 illustrates an embodiment of a bank (M×N) of cells.

FIG. 5 illustrates a 128 k array implemented as sixteen bank8k elements.

FIG. 6 illustrates a 512 k array implemented as an 8×8 array of bank8kelements.

FIG. 7 illustrates an embodiment of a bank8k block.

FIG. 8 illustrates an embodiment of a scan sequence.

FIG. 9 illustrates an embodiment of a scan sequence.

FIG. 10 illustrates that a fraction of the array may be scanned at atime.

FIG. 11 illustrates an embodiment of a circuit for measuring the currentin a cell.

FIG. 12 illustrates an embodiment of a circuit for measuring the currentin a cell.

FIG. 13 illustrates an embodiment of a circuit for measuring the currentin a cell.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

Nanopore membrane devices having pore sizes on the order of 1 nanometerin internal diameter have shown promise in rapid nucleotide sequencing.When a voltage potential is applied across a nanopore immersed in aconducting fluid, a small ion current attributed to the conduction ofions across the nanopore can be observed. The size of the current issensitive to the pore size. When a molecule, such as a DNA or RNAmolecule, passes through the nanopore, it can partially or completelyblock the nanopore, causing a change in the magnitude of the currentthrough the nanopore. It has been shown that the ionic current blockadecan be correlated with the base pair sequence of the DNA or RNAmolecule.

FIG. 1 illustrates a single stranded DNA (ssDNA) molecule constrained ina nanopore in a cell 100. As shown in FIG. 1, an anchored ssDNA molecule102 is constrained within a biological nanopore 104 opening through aninsulating membrane 106 (such as a lipid bilayer) formed above a sensorelectrode.

A nanopore based sequencing chip incorporates a large number ofautonomously operating sensor cells configured as an array. For example,an array of one million cells may include 1000 rows*100 columns ofcells. This array enables the parallel sequencing of single stranded DNA(ssDNA) molecules by measuring the conductance difference betweenindividual bases at the constriction zone of a nanopore entangledmolecule. In some embodiments, non-linear (voltage dependent)conductance characteristics of the pore-molecular complex may bedetermined for distinguishing the specific nucleotide bases at a givenlocation.

The nanopore array also enables parallel sequencing using the singlemolecule nanopore-based sequencing by synthesis (Nano-SBS) technique.FIG. 2 illustrates an embodiment of a cell 200 performing nucleotidesequencing with the Nano-SBS technique. In the Nano-SBS technique, atemplate 202 to be sequenced and a primer are introduced to cell 200. Tothis template-primer complex, four differently tagged nucleotides 208are added to the bulk aqueous phase. As the correctly tagged nucleotideis complexed with the polymerase 204, the tail of the tag is positionedin the vestibule of nanopore 206. The tails of the tags can be modifiedto have strong affinity with the amino acid residues in the vestibule ofnanopore 206. After polymerase catalyzed incorporation of the correctnucleotide, the tag-attached polyphosphate is released and will passthrough nanopore 206 to generate a unique ionic current blockade signal210, thereby identifying the added base electronically due to the tags'distinct chemical structures.

FIG. 3 illustrates four physical states of a sensor cell. The fourphysical states are hereinafter referred to as PS1-PS4. In the PS1state, a cell has no lipid bilayer formed. In the PS2 state, a lipidbilayer has been formed but a nanopore on the lipid bilayer has not beenformed yet. In the PS3 state, both a lipid bilayer and a nanopore havebeen formed. In the PS4 state, a molecule or a molecular complex (e.g.,an ssDNA molecule or a tagged nucleotide) is interacting with thenanopore. After a sensor cell transits to the PS4 state, sequencingmeasurements may be obtained.

An electrode potential is applied to each cell in the array to move thephysical state sequentially from PS1 to PS4. In some embodiments, fourpossible voltages may be applied to each of the cells in order tosupport the following transitions:

PS1->PS2

PS2->PS3

PS3->PS4

PSx->PSx (No transition)

In some embodiments, precise control of a piecewise linear voltagewaveform stimulus applied to the electrode is used to transition thecells through different physical states.

The physical state of each cell can be determined by measuring acapacitance. In addition, the physical state can be determined bymeasuring a current flow when a bias voltage (e.g., ˜50-150 mV) isapplied.

In some embodiments, the electrode voltage potential is controlled andthe electrode current is monitored simultaneously. In some embodiments,each cell of the array is controlled independently from others dependingon the physical state of the cell. The independent control of a cellfacilitates the management of a large number of cells that may be indifferent physical states.

In some embodiments, circuit simplification and circuit size reductionis achieved by constraining the allowable applied voltages at any giventime to two and iteratively transitioning the cells of the array inbatches between the physical states. For example, the cells of the arraymay be initially divided into a first group with cells in the PS1 stateand a second group with cells in the PS2 state. The first group includescells that do not have a bilayer already formed. The second groupincludes cells that have already had a bilayer formed. Initially, thefirst group includes all the cells in the array and the second groupincludes no cells. In order to transition the cells from the PS1 stateto the PS2 state, a lipid bilayer formation electric voltage is appliedto the cells. Measurements (e.g., current or capacitance measurements)are then performed to determine whether lipid bilayers have been formedin the cells. If the measurement corresponding to a cell indicates thata lipid bilayer has been formed, then the cell is determined as havingtransitioned from the PS1 state to the PS2 state, and the cell is movedfrom the first group to the second group. Since each of the cells in thesecond group has a lipid bilayer already formed, the cells in the secondgroup no longer need to have the lipid bilayer formation electricvoltage further applied. Therefore, a zero volt bias may be applied tothe cells in the second group in order to effect a null operation (NOP),such that the cells remain in the same state. The cells in the firstgroup do not have lipid bilayers already formed. Therefore, the lipidbilayer formation electric voltage is further applied to the cells inthe first group. Over time, cells move from the initial PS1 state to thePS2 lipid bilayer state, and the above steps are halted once asufficient percentage of the cells are in the PS2 state.

Similarly, cells can be iteratively electro-porated until a sufficientpercentage has transitioned from the PS2 state to the PS3 state or fromthe PS3 state to the PS4 state.

In some embodiments, the nanopore array is divided into banks of cells.FIG. 4 illustrates an embodiment of an M×N bank of cells. Row and columnselect lines are used to control the states of the individual cells. Mand N may be any integer numbers. For example, a bank that is 8 k insize (referred to as a bank8k) may include 64×128 cells.

Since each bank is autonomous, the nanopore array can be scaled byadding additional banks For example, a 128 k array can be implemented assixteen bank8k elements as shown in FIG. 5. A 512 k array can beimplemented as an 8×8 array of bank8k elements as shown in FIG. 6. Insome embodiments, the nanopore array may be scaled to include millionsof cells. A small global control block may be used to generate controlsignals to select the banks and to set the cell applied voltage.

FIG. 7 illustrates an embodiment of a bank8k block. The bank8k buildingblock may be configured as 64 rows by 128 columns as shown in FIG. 7.Each bank8k block can be a complete sub-system with row and columnaddressing logic for reading/scanning, write address decoders,analog-to-digital converters (ADCs), and double buffered output.

In some embodiments, the read path and the write path of the bank8kblock are separate and operate in a time multiplexed fashion. Forexample, a read is followed by a write. Each row is scanned byperforming an analog-to-digital conversion of all of the cells in therow. Subsequently, software may optionally write a value to any cells inthe same row in order to update the state, thereby selecting between twodifferent applied voltages.

Each bank8k block incorporates eight ADCs 702 with each ADC 702connected to 16 columns. A column counter (colcnt) 704 generates a 16bit column select bus (csel) 706. The csel bus 706 controls eightseparate 16:1 analog muxes 708 and selects which of the 16 columns iselectrically connected to the ADCs 702. The ADC 702 outputs are latchedinto a register (not shown) that drive the low-voltage differentialsignal (LVDS) outputs. Note that the sequential cells read from a givenrow are physically located as col0, col16, . . . col112, col1, col17, .. . , and so on. The data is striped across the array with 16 bits.Similarly, the 16 bit data is written to the cells as:d[0:7]→{col0, col16,..., col112}d[8:15]→{col1, col17,..., col113}In scan mode, all banks that are enabled are read out in parallel.

In some embodiments, scanning of a row requires reading 16 columns, witheach column requiring 16 clock cycles. Thus, all cells in a row are readin 256 clocks, or 2 μs at a 128 MHz clock rate. The precharge periodoccurs immediately after a row has been scanned and lasts for 2 μs.

The bank8k is fully synchronous with all signals captured on the risingedge of the clocks, including ast 710, wr 712, and multiplexed addressdata bus 714 (ad[15:0]). During the first clock cycle, ad[15:0] isdriven with the write address which is captured by the address latch 716(alat) on the rising edge of the clock when address strobe 710 (ast)signal is high. Seven latched address (la) 718 bits are decoded todetermine to which bank and word data is written. During the secondclock cycle, ad[15:0] should be driven with the data and the wr 712signal should be asserted high to indicate that this is a data writecycle. Thus, a normal write requires two cycles: the address cycle(indicated by the ast 710 signal), followed by the data cycle (indicatedby the wr 712 signal).

There are three types of writes:

-   -   Bank Enable Register Write    -   Control Register write    -   Bank Cell A/B Select Write

Some of the bits of the latched address 718, la[8:7], are used todetermine the type of write, as shown in Table 1 below:

TABLE 1 Ia[8:7] Type of Write 00 Cell A/B Select 01 Bank Enable Register10 Control Register

The row select (rs) shift register 720 logic and the column counter 704(colcnt) together operate to perform a raster scan of all the cells inthe bank8k block. After a full integration period, a row is read out byasserting the row select 722 (rs) signal high. Together, the row select722 and column select 704 enable a single cell to drive a given column.Eight columns within a row are read out in parallel, each connected to adifferent ADC. A selected cell drives the voltage on an integratingcapacitor onto the column line using an in-cell source followeramplifier.

The row select logic is a 64 bit shift register (sr64 register 720)duplicated within every bank8k block. After all columns in a row havebeen read, an external FPGA (field-programmable gate array) may assertthe nxtrow signal 724, which causes the sr64 register 720 to shift. Oncethe entire sub-windowed field has been scanned, the external FPGAasserts the nxtscan 726, which resets the sr64 register 720 back to rowzero by shifting 1 bit into the first flip flop. By changing the periodand the duration of the nxtrow 724 and nxtscan 726 signal, the arraybeing scanned can be windowed, as will be described in greater detailbelow.

Precharging occurs on a row by row basis. A row goes into the prechargemode immediately after a row has been sampled by the ADCs. Each row hasa flip flop that samples the row enable signal when nxtrow 724 signal isasserted.

In addition, the row select shift register 720 is also used to generatethe row precharge signal by connecting the n^(th) precharge signal tothe (n+1)^(th) row select signal:Pre[n]=rs[n+1]

A row is precharged during the row scanning period immediately after ithas been read. This bit shifted precharge connection is implemented as amodulo 64 operation, and thus precharge[63] is logically connected tors[0].

FIG. 8 illustrates an embodiment of a scan sequence. After all 64 rowshave been read (along with any intervening writes), the nxtscan signalis asserted to restart the scanning process at row 0.

FIG. 9 illustrates an embodiment of a scan sequence. Correlated doublesampling (CDS) is enabled by asserting a CDS pin. In a normalmeasurement mode without CDS, the voltage on the capacitor is measured,and subsequently the nxtrow pin is asserted so that the next row can beread. Row N is pre-charged while Row N+1 is being read. Thus, a row isreset immediately after it has been read. Asserting the CDS pin allowsthe row that has just been precharged to be read. Thus, the value of thereset voltage can be read immediately after precharging is done andsubsequently read again at a later time. By subtracting the twomeasurements, the kT/C thermal noise of the precharge transistor 1114 isreduced. In addition, charge sharing voltage divider effects between theintegrator capacitance and the active follower in the cell are alsoreduced. Note that when correlated double sampling is performed, theeffective measurement rate is reduced by half, since two ADC conversionsare required for each integrated current measurement.

The row and column addresses are controlled by the nxtrow 724 andnxtscan 726 signals. Asserting the nxtrow 724 input high causes thecolumn address and the shift register to be reset to 0 and the rowaddress to be shifted by one. Asserting the nxtscan 726 input highcauses the row and column addresses to be reset to 0.

In a normal operation, the entire 8 K cell array within each bank isscanned. The ADC requires 16 clock cycles to perform a conversion, and16 such conversions are performed in order to convert an entire row.Thus, each row requires 256 clock cycles (2.0 μs @ 128 MHz).

Thus, in order to scan the entire 8K cell array, the nxtrow 724 signalis asserted every 256 cycles and the nxtscan 726 signal is asserted forone cycle in every 16,384 cycles. Using a typical clock running at 128MHz yields a sample rate of 7.8 kHz (128 μs period). It is howeverpossible to tradeoff the number of scanned cells for a higher scan rateby scanning a subset of the array. For example, the top one-quarter ofrows of the array may be scanned by asserting the nxtscan 726 signalafter 2048 clocks, as shown in FIG. 10. The sampling rate is increasedby four times, from ˜8 kHz to ˜32 kHz. However, the integration time andthe voltage signal are reduced by 4 times as well, causing degradationof the signal-to-noise ratio (SNR).

In the above example, one quarter of the array is scanned. However, alarger or a smaller fraction of the array may be scanned at a time. Forexample, ½ or ⅓ of the rows of the full array may be scanned at a time.

In the above example, three-quarters of the array is left unscanned. Insome embodiments, the entire array is scanned in multiple passes. Thefirst pass is as described above. The second pass leaves the nxtrow 724signal asserted for 16 consecutive clock cycles to bypass the first 16rows and start a new scan on the 17^(th). Scanning of the next quarterof the array is then performed normally before asserting the nxtscan 726to reset the scan shift registers. The third quarter skips 32 rows andstarts scanning on the 33^(rd) to scan the final 16 rows.

Thus, by time-interleaving, the entire array is scanned at a much higherrate than normal. The actual sample rate is not improved, since the timerequired to scan all four quarters of the array does not change. Thereare effectively “dead times” inserted between each of the quartilescans. In some cases, the current is such that the voltage measurementsaturates at the normal 8 kHz scanning rate. Thus, by time-interleavingfaster scans, readings of these high current cells in the array areobtained without saturating. The software needs to be cognizant of theprecharge signal and perform a double scan of the desired region.

In each cell, current is measured at different applied voltages. Thecell includes a circuitry to apply a constant voltage (DC voltage) or analternating voltage waveform (AC voltage) to the electrode and measure alow level current simultaneously.

In some embodiments, a voltage potential is applied to the liquidcontained within a conductive cylinder mounted to the surface of thedie. This “liquid” potential is applied to the top side of the pore andis common to all cells in the array. The bottom side of the pore has anexposed electrode, and each sensor cell can apply a distinct bottom sidepotential to its electrode. The current is measured between the topliquid connection and each cell's electrode connection on the bottomside of the pore. The sensor cell measures the current travellingthrough the pore as modulated by the molecular complex constrictedwithin the pore.

FIG. 11 illustrates an embodiment of a circuit for measuring the currentin a cell. The circuit is electrically connected to an electrochemicallyactive electrode (e.g., AgCl) through an electrode-sense (ELSNS) node1102. The circuit includes a transistor 1104. Transistor 1104 may be anNMOS or n-channel MOSFET (metal-oxide-semiconductor field-effecttransistor) that performs two functions. A controlled voltage potentialcan be applied to ELSNS node 1102, and the controlled voltage potentialcan be varied by changing the voltage on the input to an op-amp 1108controlling transistor 1104, which acts as a source follower. Transistor1104 also operates as a current conveyer to move electrons from acapacitor 1106 to ELSNS node 1102 (and vice versa). Current from thesource pin of transistor 1104 is directly and accurately propagated toits drain pin, accumulating charges on capacitor 1106. Thus, transistor1104 and capacitor 1106 act together as an ultra-compact integrator(UCI).

The UCI is used to determine the current sourced from or sunk to theelectrode by measuring the change in voltage integrated onto capacitor1106 according to the following:

I*t=C*ΔV where, I: Current

-   -   t: integration time    -   C: Capacitance    -   ΔV: voltage change

Typical operation involves precharging capacitor 1106 to a known andfixed value (e.g., V_(DD)=1.8 V), and then measuring the voltage changeat a fixed interval t. For an 8K bank operating at 128 MHz, each cellintegrates for ˜128 μs. In one example:

C = 5  fF I = 20  pA t = 128  µs $\begin{matrix}{{\Delta\; V} = {I*{t/C}}} \\{= {20\mspace{14mu}{pA}*128\mspace{14mu}{{µs}/22}\mspace{14mu}{fF}}} \\{= {512\mspace{14mu}{mV}}}\end{matrix}$In this example, the voltage swing is relatively small, and theresolution of the ADC is on the order of millivolts. The integratedvoltage may be increased by reducing the clock rate to less than 128MHz, thereby increasing the integration period.

In the above circuit, the maximum voltage swing is ˜1V, and thus thecircuit saturates with a current higher than ˜32 pA. The saturationlimit can be increased by reducing the scan window to effectivelyincrease the cell scan rate. By interleaving fast and slow scans, thedynamic range of the current that can be measured can be increased.

Transistor 1104 acts as a current conveyor by moving charges from theintegrating capacitor 1106 to the electrode. Transistor 1104 also actsas a voltage source, imposing a constant voltage on the electrodethrough the opamp feedback loop. The column drive transistor 1110 isconfigured as a source follower in order to buffer the capacitor voltageand provide a low impedance representation of the integrated voltage.This prevents charge sharing from changing the voltage on the capacitor.

Transistor 1112 is a transistor connected to the row select (rs) signal.It is used as a row access device with the analog voltage output at itssource connected as a column shared with many other cells. Only a singlerow of the column connected AOUT signal is enabled so that a single cellvoltage is measured.

In an alternative embodiment, the row select transistor (transistor1112) may be omitted by connecting the drain of the column drivetransistor 1110 to a row selectable “switched rail.”

A precharge transistor 1114 is used to reset the cell to a predeterminedstarting voltage from which the voltage is integrated. For example,applying a high voltage (e.g., V_(DD)=1.8 V) to both vpre and pre willpull capacitor 1106 up to a precharged value of (V_(DD)−V_(t)). Theexact starting value can vary both from cell to cell (due to V_(t)variation of precharge transistor 1114) as well as from measurement tomeasurement, due to the reset switch thermal noise (sqrt(kTC) noise). Itis possible to eliminate this V_(t) variation by limiting the prechargevoltage to less than V_(DD)−V_(t). In this case, the prechargetransistor 1114 will pull all the way up to the vpre voltage. Even inthis case, however, the kT/C noise is still present. As a result, acorrelated double sampling (CDS) technique is used to measure theintegrator starting voltage and the ending voltage to determine theactual voltage change during the integration period. CDS is accomplishedby measuring the voltage on the integrating capacitor 1106 twice: onceat the beginning and once at the end of the measurement cycle.

Note also that the drain of precharge transistor 1114 is connected to acontrolled voltage vpre (reset voltage). In a normal operation, vpre isdriven to a fixed voltage above the electrode voltage. However, it canalso be driven to a low voltage. If the vpre node of prechargetransistor 1114 is in fact driven to ground, then the current flow isreversed (i.e., current flows from the electrode into the circuitthrough transistor 1104 and precharge transistor 1114), and the notionof source and drain is swapped. The negative voltage applied to theelectrode (with respect to the liquid reference) is controlled by thevpre voltage, assuming that the gate voltages of transistors 1114 and1104 are at least greater than vpre by a threshold. Thus, a groundvoltage on vpre can be used to apply a negative voltage to theelectrode, for example to accomplish electroporation or bilayerformation.

An ADC measures the AOUT voltage immediately after reset and again afterthe integration period (i.e., performs the CDS measurement) in order todetermine the current integrated during a fixed period of time. An ADCcan be implemented per column. A separate transistor may be used foreach column as an analog mux to share a single ADC between multiplecolumns. The column mux factor can be varied depending on therequirements for noise, accuracy, and throughput.

In some alternative embodiments, the op-amp/transistor combination asshown in FIG. 11 may be replaced by a single transistor as shown in FIG.12.

FIG. 13 illustrates an alternative embodiment of a circuit for measuringthe current in a cell. The circuit includes an integrator, a comparator,and digital logic to shift in control bits and simultaneously shift outthe state of the comparator output. The B0 through B1 lines come out ofthe shift register. The analog signals are shared by all cells within abank, and the digital lines are daisy-chained from cell to cell.

The cell digital logics include a 5 bit data shift register (DSR), 5 bitparallel load registers (PLR), control logic, and an analog integratorcircuit. Using the LIN signal, the control data shifted into the DSR isloaded in parallel into the PLR. The 5 bits control digital“break-before-make” timing logic controls the switches in the cell. Thedigital logic has a set-reset (SR) latch to record the switching of thecomparator output.

The architecture in FIG. 13 delivers a variable sample rate that isproportional to the individual cell current. A higher current results inmore samples per second than a lower current. The resolution of thecurrent measurement is related to the current being measured. A smallcurrent is measured with a finer resolution than a large current, whichis a clear benefit over fixed resolution measurement systems. An analoginput may be used to adjust sample rates by changing the voltage swingof the integrator. Thus, it is possible to increase the sample rate inorder to analyze biologically fast processes or to slow the sample rate(thereby gaining precision) in order to analyze biologically slowprocesses.

The output of the integrator is initialized to a low voltage bias (LVB)and integrates up to a voltage CMP. A sample is generated every time theintegrator output swings between these two levels. Thus, the greater thecurrent, the faster the integrator output swings and therefore thefaster the sample rate. Similarly, if the CMP voltage is reduced, theoutput swing of the integrator needed to generate a new sample isreduced and therefore the sample rate is increased. Thus, simplyreducing the voltage difference between LVB and CMP provides a mechanismto increase the sample rate.

Using the architecture as shown in FIG. 13, an integrator and acomparator are used at each cell site. The current being measured isintegrated, creating a voltage ramp at the output of the integrator.When this voltage reaches a predetermined value (the comparatorthreshold), a flag is sent to a circuitry on the periphery of the array.The number of clock pulses counted between the initiation of theintegrator ramp and the tripping of the comparator is a measure of thecurrent value. The conversion time is thus a variable.

Using the architecture as shown in FIG. 11, the integrator ramps for aconfigurable fixed period of time. At the beginning and at the end ofthat time, an ADC on the periphery of the array measures the voltage.Advantages of the architecture in FIG. 11 include: 1) The amount ofcircuitry at each site is less because there is no comparator; and 2)Having a configurable fixed conversion time is desirable when dealingwith large amount of data generated by denser arrays (e.g., 100,000 to1,000,000 sites or more).

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A device comprising: a plurality of measurementcells, each measurement cell including a cell electrode above which ananopore is formed, the cell electrode configurable to apply a distinctpotential that is independent from cell electrodes in other measurementcells, each measurement cell including an integrator electronicallycoupled to the cell electrode; a common electrode, the common electrodeconfigured to apply a common potential to a liquid above the nanoporesformed above the cell electrodes in the plurality of measurement cells,wherein the common potential is common to all of the measurement cells,and wherein the integrator in each measurement cell measures the currentflowing between the common electrode and the cell electrode in themeasurement cell; a plurality of analog-to-digital converters, whereinan integrator from the plurality of measurement cells is electricallycoupled to one analog-to-digital converter of the plurality ofanalog-to-digital converters.
 2. The device of claim 1, wherein eachmeasurement cell further includes a liquid chamber containing theliquid.
 3. The device of claim 2, wherein, the common electrode suppliesa common electric potential when the liquid chamber contains anelectrolyte, the cell electrode supplies a variable electric potentialwhen the liquid chamber contains the electrolyte, wherein the voltagebetween the common electrode and the cell electrode equals the variableelectric potential minus the common electric potential, the integratorincludes an integrating capacitor, the voltage across the integratingcapacitor is a measure of the current flowing between the commonelectrode and the cell electrode during a measurement period, and thevariable electric potential of the cell electrode is controlled by anapplied voltage.
 4. The device of claim 3, wherein the variable electricpotential of the cell electrode is controlled by the applied voltage viaa buffering means.
 5. The device of claim 1, wherein the integratorfurther includes: a buffering component, wherein the buffer component iselectrically coupled to the analog-do-digital converter to buffer anoutput of the integrator before being connected to the analog-do-digitalconverter.
 6. The device of claim 1, wherein the analog-to-digitalconverter coupled to the integrator measures a first voltage at anoutput of the integrator at a beginning of a measurement period and asecond voltage at the output of the integrator at an end of themeasurement period, and wherein a difference of the second voltage andthe first voltage corresponds to a measurement of the current.
 7. Thedevice of claim 6, wherein the measurement period is adjusted based atleast in part on the current and how much time the current would take tocause a saturation.
 8. The device of claim 1, wherein, more than oneintegrators send their output to a coupled analog-to-digital convertercorresponding to the more than one integrators via a time-divisionmultiplexing channel.
 9. The device of claim 1, wherein at least one ofthe analog-to-digital converters includes a comparator.
 10. The deviceof claim 9, wherein the analog-to-digital converter includes acontrolling analog input, and the controlling analog input controls avariable sample rate of the current measurement by varying a voltage atthe controlling analog input.
 11. The device of claim 10, wherein thevariable sample rate increases when the current increases.
 12. Thedevice of claim 10, wherein the varied voltage comprises a comparatorthreshold.
 13. The device of claim 10, wherein the varied voltagecomprises an initial voltage at an output of one of the integrators. 14.The device of claim 13, wherein a time measurement of the output of oneof the integrators to reach a comparator threshold from the initialvoltage corresponds to a measurement of the current.
 15. The device ofclaim 1, wherein, a column of integrators from the plurality ofmeasurement cells is electrically coupled to one analog-to-digitalconverter of the plurality of analog-to-digital converters, and thecolumn of integrators share the coupled analog-to-digital converter viaa time-division multiplexing channel.
 16. The device of claim 2, whereinthe device is configured to retain at least one lipid, one nanoporeprotein, and one molecular complex in the liquid chamber of at least onemeasurement cell of the plurality of measurement cells.
 17. The deviceof claim 16, wherein the molecular complex comprises one of thefollowing: a single stranded DNA, a single stranded RNA, and a taggednucleotide.
 18. The device of claim 16, wherein the device is configuredto supply an electrical stimulus to the lipid, the nanopore protein, andthe molecular complex in the liquid chamber of at least one measurementcell of the plurality of measurement cells.
 19. The device of claim 16,wherein, the device is configured to individually detect a physicalstate and individually transpose the physical state from a plurality ofpossible physical states of a material in the liquid chamber of eachmeasurement cell of the plurality of measurement cells, by modulatingthe voltage and measuring the current between the common electrode andthe cell electrode, and the plurality of possible physical statescomprises: no formation of a lipid bilayer, formation of a lipidbilayer, insertion of a nanopore protein in a lipid bilayer, forming ananopore, and interaction of a molecular complex with the nanopore. 20.The device of claim 19, wherein each measurement cell progresses throughthe plurality of possible physical states at an own pace of saidmeasurement cell, independently of the physical states of othermeasurement cells of the plurality of measurement cells.
 21. The deviceof claim 16, wherein the device is configured to recognize a specificbase type corresponding to the molecular complex in the liquid chamberof one measurement cell of the plurality of measurement cells bymeasuring the current flowing between the common electrode and the cellelectrode.
 22. The device of claim 2, wherein the current between thecommon electrode and the cell electrode flows in either directiondepending on a controlling potential applied to a terminal of theintegrator.